Several years ago we discovered a new form of diacylglycerol kinase that preferentially catalyses the phosphorylation of diacylglycerol molecular species that contain esterified arachidonic acid. We also showed that high amounts of the enzyme are present in the testis and brain of the mature baboon. Since then we have been exploring the possibility that the enzyme may play a role in cell signaling processes that involve inositol-containing phophoglycerides. We have shown that the enzyme is present in preparations of synaptosomes and have also shown that the enzyme is present in very high concentrations in the macaque retina. This latter finding is of particular interest because it raises the possibility that phosphatidylinositol-dependent cell signaling may play a role in the visual process. What is needed now is to localize the enzyme in specific cells and cell membranes of the retina, and we will need specific antibodies for this immunochemical localization work. We have prepared antibodies directed to specific regions of the enzyme's sequence, and have used these antibodies in Western blotting experiments. But we have not yet succeeded in using them for immunochemical localization work. It may be that we will have to prepare monoclonal antibodies to the enzyme in the future.